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Commit c84cdf75 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Tejun Heo
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cgroup: Remove unnecessary task_lock before fetching css_set on migration 



When we fetch the css_set of the tasks on cgroup migration, we don't need
anymore to synchronize against cgroup_exit() that could swap the old one
with init_css_set. Now that we are using threadgroup_lock() during
the migrations, we don't need to worry about it anymore.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: default avatarMandeep Singh Baines <msb@chromium.org>
Reviewed-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Containers <containers@lists.linux-foundation.org>
Cc: Cgroups <cgroups@vger.kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
parent 7e381b0e

kernel/cgroup.c

+10 −10
Original line number Diff line number Diff line
@@ -1850,14 +1850,14 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, 
	struct css_set *newcg;



	/*

	 * get old css_set. we need to take task_lock and refcount it, because

	 * an exiting task can change its css_set to init_css_set and drop its

	 * old one without taking cgroup_mutex.

	 * get old css_set. We are synchronized through threadgroup_lock()

	 * against PF_EXITING setting such that we can't race against

	 * cgroup_exit() changing the css_set to init_css_set and dropping the

	 * old one.

	 */

	task_lock(tsk);

	WARN_ON_ONCE(tsk->flags & PF_EXITING);

	oldcg = tsk->cgroups;

	get_css_set(oldcg);

	task_unlock(tsk);



	/* locate or allocate a new css_set for this task. */

	if (guarantee) {
@@ -1879,9 +1879,7 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, 
	}

	put_css_set(oldcg);



	/* @tsk can't exit as its threadgroup is locked */

	task_lock(tsk);

	WARN_ON_ONCE(tsk->flags & PF_EXITING);

	rcu_assign_pointer(tsk->cgroups, newcg);

	task_unlock(tsk);
@@ -2182,11 +2180,13 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) 
		/* nothing to do if this task is already in the cgroup */

		if (tc->cgrp == cgrp)

			continue;

		/* get old css_set pointer */

		task_lock(tc->task);

		/*

		 * get old css_set pointer. threadgroup is locked so this is

		 * safe against concurrent cgroup_exit() changing this to

		 * init_css_set.

		 */

		oldcg = tc->task->cgroups;

		get_css_set(oldcg);

		task_unlock(tc->task);

		/* see if the new one for us is already in the list? */

		if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) {

			/* was already there, nothing to do. */